(CNN) -- A black Louisiana teenager at the center of the racially charged "Jena 6" case was ordered Thursday to spend 18 months in a juvenile facility, after a judge ruled he had violated his probation for earlier juvenile convictions, a source with knowledge of the court proceedings said.

Supporters joined Mychal Bell after he was released from jail last month.

Mychal Bell, 17, who was freed two weeks ago after his adult criminal conviction for beating a white classmate was overturned, was sent to the Renaissance Home for Youth in Alexandria, Louisiana, the source said.

The decision came at the end of a two-day juvenile court hearing that was closed to the media and public.

Carol Powell-Lexing, one of Bell's attorneys, said the judge's decision would be appealed.

Bell was freed on $45,000 bail on September 27, after an appeals court threw out his conviction on battery and conspiracy charges in adult court and remanded the case to juvenile court.

But Judge J.P. Mauffrey agreed with prosecutors that Bell had violated the probation he was given for four previous juvenile offenses, including two simple battery charges, the sources said.

Bell had been placed on probation until he turned 18.

Civil rights activist Al Sharpton, who has championed Bell's case, denounced Thursday's decision as "revenge" by the judge and called on Louisiana Gov. Kathleen Blanco to intervene.

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Demonstrators in September took to the streets of the small town of Jena to protest how authorities handled the cases of Bell and five other teens accused of beating white student Justin Barker in December 2006. The incident was a culmination of fights between blacks and whites.

Many said they were angry that the students, dubbed the "Jena 6," were being treated more harshly than three white students who hung nooses from an oak tree on Jena High School property.

The white students were suspended from school but did not face criminal charges. The protesters said they should have been charged with a hate crime. E-mail to a friend